1. Field of the Invention
The present invention relates to strip lights and more particularly to such a strip light having an arrangement for supplying a constant current to each illuminator thereof.
2. Description of Related Art
A conventional LED (light-emitting diode) based strip light is disclosed in Taiwanese Patent Published No. 516,709 (the prior art). The prior art comprises a plurality of LEDs (light emitting diodes) mounted on a circuit board, a plurality of resistors coupled to each of the LEDs on the circuit board, two diodes at both ends of the circuit board, a positive terminal at one end of the circuit board for coupling to another LED based strip light or power source, a negative terminal at the other end of the circuit board for coupling a positive terminal of another LED based strip light or power source, upper insulation means for enclosing the LEDs, the resistors, the diodes, and the positive and the negative terminals on a top surface of the circuit board, and lower insulation means for enclosing pins, contacts, and circuits on a bottom surface of the circuit board.
The prior art is adapted to regulate current. However, the prior art suffered from several disadvantages. For example, high heat can be generated by a LED and its coupled resistor. Such heat may be excessively high if the number of LEDs and thus the number of resistors are large (i.e., many LEDs and resistors are coupled in series). Also, brightness of the LEDs can be lowered due to increased resistance. In other words, a considerable portion of electrical energy is consumed (i.e., wasted) by resistors rather than by LEDs. Further, brightness of one LED may be different from that of other LEDs due to uneven resistor in respective LEDs.
U.S. Pat. No. 4,717,868 entitled “Uniform Intensity led Driver Circuit” discloses the following characteristics. Voltage from a string of LEDs is fed to an output terminal 19. The voltage is decreased by a resistor R2 prior to turning on transistors Q3, Q4, and Q7. Further, high and low voltage levels are controlled by a node 13 for turning on transistor Q1 and for inputting signal through a NOR gate 17 and an inverter 16. Another signal through the NOR gate 17 is fed to a node 14 which is adapted to control high and low voltage levels for turning on transistor Q6. A comparison signal is generated by a comparator 15 in response to feeding two voltage signals from nodes 27 and 28 and comparing same. Further, the comparison signal is fed to the NOR gate 17 and high or low voltage level is fed to the NOR gate 17 via node 13 respectively for turning on transistor Q5 or not. As a result, the LEDs can maintain its constant current state. However, nodes 13 and 14 for high or low voltage level control, and NOR gate 17 for operation and output are required by the patent and thus the patent does not respond to temperature change. Also, no overload protection is provided. Further, PWM (pulse width modulation) for constant current control is not applicable to the patent. This is not desirable. Thus, the need for improvement still exists.